P-660 Series Support Notes
There are two versions of SNMP: Version 1 and Version 2. ZyXEL supports
SNMPv1. Most of the changes introduced in Version 2 increase SNMP's security
capabilities. SNMP encompasses three main areas:
1. A small set of management operations.
2. Definitions of management variables.
3. Data representation.
The operations allowed are: Get, GetNext, Set, and Trap. These functions operates
on variables that exist in network nodes. Examples of variables include statistic
counters, node port status, and so on. All of the SNMP management functions are
carried out through these simple operations. No action operations are available, but
these can be simulated by the setting of flag variables. For example, to reset a node, a
counter variable named 'time to reset' could be set to a value, causing the node to reset
after the time had elapsed.
SNMP variables are defined using the OSI Abstract Syntax Notation One (ASN.1).
ASN.1 specifies how a variable is encoded in a transmitted data frame; it is very
powerful because the encoded data is self-defining. For example, the encoding of a
text string includes an indication that the data unit is a string, along with its length and
value. ASN.1 is a flexible way of defining protocols, especially for network
management protocols where nodes may support different sets of manageable
variables.
The net of variables that each node supports is called the Management Information
Base (MIB). The MIB is made up of several parts, including the Standard MIB,
specified as part of SNMP, and Enterprise Specific MIB, which are defined by
different manufacturer for hardware specific management.
The current Internet-standard MIB, MIB-II, is defined in RFC 1213 and contains 171
objects. These objects are grouped by protocol (including TCP, IP, UDP, SNMP, and
other categories, including 'system' and 'interface.'
The Internet Management Model is as shown in figure 1. Interactions between the
NMS and managed devices can be any of four different types of commands:
Reads
Read is used to monitor the managed devices, NMSs read variables that are
maintained by the devices.
Writes
Write is used to control the managed devices, NMSs write variables that are
stored in the managed devices.
73
All contents copyright © 2005 ZyXEL Communications Corporation.
To Next Page
Loading...
